1. Field of the Invention
This invention relates to new and useful improvements in diamond drill bits and particularly to bits in which the bit body has a carbide coated cutting face.
2. Brief Description of the Prior Art
Rotary drill bits used in earth drilling are primarily of two major types. One major type of drill bit is the roller cone bit having three legs depending from a bit body which support three roller cones carrying tungsten carbide teeth for cutting rock and other earth formations. Another major type of rotary drill bit is the diamond bit which has fixed teeth of industrial diamonds supported on the drill body or on metallic or carbide studs or slugs anchored in the drill body.
There are several types of diamond bits known to the drilling industry. In one type, the diamonds are a very small size and randomly distributed in a supporting matrix. Another type contains diamonds of a larger size positioned on the surface of a drill shank in a predetermined pattern. Still another type involves the use of a cutter formed of a polycrystalline diamond supported on a sintered carbide support.
Some of the most recent publications dealing with diamond bits of advanced design, relevent to this invention, consists of Rowley, et al. U.S. Pat. No. 4,073,354 and Rohde, et al. U.S. Pat. No. 4,098,363. An example of cutting inserts using polycrystalline diamond cutters and an illustration of a drill bit using such cutters, is found in Daniels, et al. U.S. Pat. No. 4,156,329.
The most comprehensive treatment of this subject in the literature is probably the chapter entitled STRATAPAX bits, pages 541-591 in ADVANCED DRILLING TECHNIQUES, by William C. Maurer, The Petroleum Publishing Company, 142l South Sheridan Road, P.O. Box 1260, Tulsa, Oklahoma, 74101, published in 1980. This reference illustrates and discusses in detail the development of the STRATAPAX diamond cutting elements by General Electric and gives several examples of commercial drill bits and prototypes using such cutting elements.
The hardfacing of roller bit bodies with tungsten carbide has been known for many years. Tungsten carbide hardfacing has been applied to the bit body prior to final assembly. Conventional hardfacing techniques, however, require the use of sufficiently high temperatures for application of the tungsten carbide coatings that the metallurgical properties of the steel body may be adversely affected. Attempts have been made to apply tungsten carbide coatings to bit bodies by conventional plasma spraying systems and by explosive-type coating methods. Such systems produce only very thin coatings and either do not adhere to the steel surface adequately or are too thin to withstand the severe conditions encountered in earth drilling.
Hardfacing of drilling tools, including tool joints, drill collars and rotary cone bits is found several places in the patent literature and summary of the art as of about 1970 is given in HISTORY OF OIL WELL DRILLING, J. E. Brantly, Gulf Publishing Co., 1971, pp. 1028, 1029, 1081.